Physiological studies on cells of Klebsiella aerogenes suggest that an enzyme, glutamine synthetase, also functions to regulate transcription of genes coding for enzymes involved in nitrogen metabolism. In the case of the hut genes, which are necessary for histidine degradation, it has been demonstrated directly, in a purified transcription system that highly purified glutamine synthetase is a positive control element which activates transcription. It has also been proposed that glutamine synthetase regulates its own synthesis by acting as an activator and, possibly also, as a repressor of glnA transcription. Our recent work shows that although glutamine synthetase activates transcription of the hut-genes, another factor is also required. Genetic evidence suggests that some additional factor is also needed for glutamine synthetase to regulate expression of the glnA gene. We propose to study the factor(s) needed for glutamine synthetase regulation of gene expression using biochemical experiments as well as genetic and physiological studies on whole cells.